Many electronic devices, such as computers, TV sets, etc. or batteries that have to be charged, require a DC voltage as an input voltage, while the supply voltage that is available from the power grid is an AC voltage. In these cases an AC/DC conversion, that converts the AC input voltage into a DC output voltage, is required. Particularly in those cases, in which the power consumption of the load is higher than several 10 Watts, additionally to the power conversion a power factor correction is required. The power factor correction serves to minimize the reactive power and to maximize the real power taken from the grid.
An AC/DC converter that provides power factor correction includes a power factor corrector (PFC) and a DC/DC converter coupled to the PFC. The PFC is usually a boost converter that generates a DC voltage that is higher than the amplitude (peak value) of the AC input voltage. The DC/DC converter converts the DC voltage provided by the PFC into a DC output voltage supplied to the load voltage. The input voltage as well as the input current of the PFC have a sine waveform. When the power factor of the PFC is close to 1, such as between 0.97 and 1, the input voltage and the input current are almost in phase, so that the input power of the PFC has a squared sine (sin2) waveform that cause ripples of the PFC output voltage. In order to reduce the amplitude of those ripples a capacitor, that is also referred to as DC link capacitor, is connected between output terminals of the PFC.
The DC link capacitor may have a capacitance of up to several mF (Millifarads) and is usually implemented as an electrolytic capacitor. However, electrolytic capacitors have a relatively short lifetime, have high leakage currents, and are expensive.
There is, therefore, a need to provide an AC/DC power converter circuit with a PFC and a DC/DC converter in which the size of the DC link capacitor can be reduced without degrading the power conversion efficiency and without increasing ripples of a DC voltage at the output of the DC/DC converter.